Animal Reproduction - Gynaecology and Obstetrics- ICAR JRF/SRF 2024

• Dystocia in Sows: In swine obstetrics, the single most common maternal cause of dystocia is uterine inertia (accounting for over $60\%\text{ to }75\%$ of all pig farrowing dystocias).
• Mechanisms: Primary uterine inertia occurs in overconditioned sows, exhausted elderly sows, or sows with hypocalcemia/hypoglycemia; secondary uterine inertia occurs after delivering multiple piglets against an obstructive fetus or prolonged farrowing exhaustion.

Correct option: (3) Uterine inertia

• Mechanism of Post-Coital Estrogen Interception: Administration of supraphysiological doses of estrogens (e.g., estradiol benzoate, diethylstilbestrol) within 1 to 3 days post-mating ('mismating shot') prevents pregnancy primarily by interfering with normal oviductal transport of embryos.
• 'Tubal Lock' Effect: Estrogen induces spastic constriction of the isthmic circular musculature and uterotubal junction ('tube locking'), trapping the developing zygotes in the ampulla until they degenerate, or conversely accelerating tubal transit prematurely before the endometrium is receptive.

Correct option: (1) Interfering with oviductal transport of embryo

• Uterine Involution in the Mare: Unlike ruminants which require 30–45 days to complete caruncular sloughing and re-epithelialization, the microcotyledonary diffuse placenta of the mare separates cleanly at parturition.
• Histological Restoration: The equine endometrium undergoes remarkably rapid regeneration, with complete histomorphological restoration of the luminal epithelium and uterine glands achieved by 13 to 14 days postpartum (13.25 days), enabling high conception rates during the subsequent foal heat.

Correct option: (3) 13.25 days